1. Field of the Invention
This invention relates to a photographic material and, in particular, to a photographic material comprising a photographic layer of a hydrophilic colloid provided on a support having a hydrophobic surface.
2. Description of the Prior Art
Polyethylene terephthalate, cellulose triacetate, polystyrene, polyolefin laminated paper, etc. have generally been used so far for conventional photographic supports because of their excellent transparency and/or flexibility. Unfortunately, all of these materials have highly hydrophobic surfaces, so that it is very difficult to adhere a photographic layer of a hydrophilic colloid, generally of gelatin, tightly on the supports.
Prior art processes, which are employed to overcome the above-described difficulty, for obtaining an effective adhesive strength between a photographic emulsion layer and the surface of the support by way of the surface treatment, particularly, a treatment for rendering the hydrophobic surface of the support hydrophilic comprise the following two types of processes:
(1) Applying a surface activation treatment such as a chemical treatment, a mechanical treatment, a corona discharge, a flame treatment, a UV irradiation, a radio-frequency treatment, a glow discharge, an active-plasma treatment, a laser treatment, a mixed acid treatment or ozone-oxidation followed by the direct coating of a photographic emulsion to provide adhesion.
(2) Providing a subbing layer after the above surface treatments and coating a photographic emulsion layer thereon (for example, as disclosed in U.S. Pat. Nos. 2,698,241, 2,764,520, 2,864,755, 2,864,756, 2,972,534, 3,057,792, 3,071,466, 3,072,483, 3,143,421, 3,145,105, 3,145,242, 3,360,448, 3,376,208, 3,462,335 and 3,475,193, and British Patent Nos. 788,365, 804,005 and 891,469).
The latter method (2) is more effective and, hence, widely used.
It is believed that in all of these surface treatments, the surface of the support is rendered hydrophilic due to the formation of polar groups, more or less, on the surface of the support which is hydrophobic in nature, etc. and, as the result, the affinity of the surface for the polar groups of the components contained in the subbing composition is increased.
Various techniques have been employed for coating a subbing layer and they include the so-called double-layer method in which a first layer exhibiting excellent adhesion to the support is provided and then a second layer of a hydrophilic resin is coated thereon, and a single layer method in which only one resin layer containing both hydrophobic groups and hydrophilic groups is coated.
All of these methods have been studied thoroughly and various resins have been examined for their suitability for use as a subbing layer, including, for example, copolymers of vinyl chloride, vinylidene chloride, methacrylic acid, acrylic acid, itaconic acid, maleic anhydride, etc., as well as polyethyleneimine, epoxy resins, grafted gelatin-nitrocellulose and the like. These methods, however, inevitably have the following defects:
(A) Insufficient adhesive strength PA0 (B) Subbing coating requires many steps and much time PA0 (C) Problems of toxic gases, skin irritation, environmental pollution, etc. PA0 (D) Unevenness of the film surface PA0 (E) Temperature control is difficult in the drying of the subbing layer
In particular, with a support of polyethylene terephthalate, polystyrene, etc., the adhesive strength obtained with only a surface activation described in (1) above can not satisfy at all the practical requirements for photographic materials. Moreover, in coating a subbing composition, a resin having a good affinity for and excellent adhesion to the hydrophobic support generally exhibits poor affinity for and only insufficient adhesion to a hydrophilic photographic layer to be coated thereon. On the contrary, a hydrophilic resin having a good affinity for the photographic layer, when used as a subbing layer, exhibits excellent adhesion to the photographic layer but insufficient adhesion to the support.
Since gelatin is often used as a resin for a photographic binder, the photographic layer is coated and dried at extremely low temperatures (for example, the gelatin is cooled to a temperature below about 10.degree. C and then dried at a temperature below about 50.degree. C), taking advantage of the specific property of gelatin of gelling at lower temperatures. However, when the above described polymers are used as a subbing layer, these polymers should be heated, after cooling, to higher temperatures, for example, about 100.degree. C or more for drying because they generally lack the property of gelling at lower temperatures. In addition, these synthetic high molecular weight compounds often require organic solvents as a solvent instead of water that can be used for gelatin. This necessitates an additional coating apparatus for such an organic solvent separate from that used for the photographic layers. These coating and drying steps must be repeated two or three times in a double subbing layer method.
For further improving the adhesive strength of the subbing layer described above, various means have been employed, for example, solvents which swell or dissolve the support or the so-called etching agents which have high polarity and a high boiling point and which are expensive have been incorporated in a large quantity into a subbing composition. For example, etching agents for polyester include compounds having an aromatic ring (such as a benzene ring, a naphthalene ring, a pyridine ring, a pyrrole ring or a condensed ring thereof, or these aromatic rings substituted with one or more of alkyl, alkoxy, acyl, nitro, cyano, hydroxy, formyl, carboxy, alkoxycarbonyl, hydroxyalkyl, aminoalkyl or haloalkyl groups, halogen atoms, or the like), alcohols, ketones, carboxylic acids, esters, aldehydes, or the like (for example, as disclosed in British Patent Nos. 772,600, 776,157, 785,789 and 797,425, U.S. Pat. No. 2,830,030, and German Patent Nos. 1,020,457 and 1,092,652). Specific examples of these etching agents are benzoic acid, salicylic acid, salicyclic acid ester, monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, trifluoroacetic acid, methanesulfonic acid, trifluoromethanesulfonic acid, nitropropanol, benzyl alcohol, benzaldehyde, acetylacetone, acetylphenol, benzamide, benzonitrile, anisole, nitrobenzyl alcohol, chlorobenzyl alcohol, pyrrole, chloral hydrate, benzylamine, xylylenediamine, nicotinic acid amide and nicotinic acid ester.
Other examples of these etching agents, which are particularly well known and generally used widely, are compounds having phenolic hydroxyl groups such as phenol, o-chlorophenol, p-chlorophenol, dichlorophenol, phenylphenol, chlororesorcin, fluoroglycine, orcinol, pyrogallol, gallic acid, o-cresol, m-cresol, p-cresol, resorcin or methoxyphenol.
It is, however, well known that these etching agents are usually difficult to handle and harmful to the human body. Further, phenolic compounds often provide serious problems in operation since they have strong irritation to and penetration into the skin. Moreover, these compounds, if contained in waste water or exhaust gases, cause a destruction of the environment and should, therefore, be substantially recovered, which requires additional waste treatment facilities.
In the prior art processes, considerably high temperatures are required for drying the subbing layer as described above in paragraphs (B) and (C).
Particularly, since phenolic compounds generally have a high boiling point above about 180.degree. C, the drying of the subbing layer of these compounds requires heating for a rather long time. Therefore, undesirably, expansion and reduction in the modulus of elasticity occur in polyesters during drying, particularly at the earlier stage of the drying, due to the increase in the degree of crystallinity caused by the penetration of the solvent into the polyester support, and shrinkage in polyesters occurs at the later stage of the drying, thereby resulting in a marked unevenness of the surface.
Since the etching capability of the solvent is highly temperature-dependent, the adhesive strength per se, if it is produced by an anchoring effect of the resin to the support, is also highly dependent on the temperatures used in the steps of coating, drying, etc.
This is a serious problem from the standpoint of production in a stable manner.